starboard/shared/win32/video_decoder.cc

// Copyright 2017 The Cobalt Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "starboard/shared/win32/video_decoder.h"

#include <functional>

#include "starboard/common/log.h"
#include "starboard/shared/win32/dx_context_video_decoder.h"
#include "starboard/shared/win32/error_utils.h"
#include "starboard/shared/win32/hardware_decode_target_internal.h"
#include "starboard/time.h"

// Include this after all other headers to avoid introducing redundant
// definitions from other header files.
#include <codecapi.h>  // For CODECAPI_*
#include <initguid.h>  // For DXVA_ModeVP9_VLD_Profile0

namespace starboard {
namespace shared {
namespace win32 {

namespace {

using Microsoft::WRL::ComPtr;
using ::starboard::shared::starboard::player::filter::VideoFrame;
using std::placeholders::_1;
using std::placeholders::_2;

// Limit the number of active output samples to control memory usage.
// NOTE: Higher numbers may result in increased dropped frames when the video
// resolution changes during playback (if the decoder is not forced to use
// max resolution resources).
const int kMaxOutputSamples = 10;

// Throttle the number of queued inputs to control memory usage.
const int kMaxInputSamples = 15;

// Prime the VP9 decoder for a certain number of output frames to reduce
// hitching at the start of playback.
const int kVp9PrimingFrameCount = 10;

// Decode targets are cached for reuse. Ensure the cache size is large enough
// to accommodate the depth of the presentation swap chain, otherwise the
// video textures may be updated before or while they are actually rendered.
const int kDecodeTargetCacheSize = 2;

// Allocate decode targets at the maximum size to allow them to be reused for
// all resolutions. This minimizes hitching during resolution changes.
#ifdef ENABLE_VP9_8K_SUPPORT
const int kMaxDecodeTargetWidth = 7680;
const int kMaxDecodeTargetHeight = 4320;
#else   // ENABLE_VP9_8K_SUPPORT
const int kMaxDecodeTargetWidth = 3840;
const int kMaxDecodeTargetHeight = 2160;
#endif  // ENABLE_VP9_8K_SUPPOR

DEFINE_GUID(DXVA_ModeVP9_VLD_Profile0,
            0x463707f8,
            0xa1d0,
            0x4585,
            0x87,
            0x6d,
            0x83,
            0xaa,
            0x6d,
            0x60,
            0xb8,
            0x9e);

DEFINE_GUID(DXVA_ModeVP9_VLD_10bit_Profile2,
            0xa4c749ef,
            0x6ecf,
            0x48aa,
            0x84,
            0x48,
            0x50,
            0xa7,
            0xa1,
            0x16,
            0x5f,
            0xf7);

scoped_ptr<MediaTransform> CreateVideoTransform(
    const GUID& decoder_guid,
    const GUID& input_guid,
    const GUID& output_guid,
    const IMFDXGIDeviceManager* device_manager) {
  scoped_ptr<MediaTransform> media_transform(new MediaTransform(decoder_guid));
  if (!media_transform->HasValidTransform()) {
    // Decoder Transform setup failed
    return scoped_ptr<MediaTransform>().Pass();
  }
  media_transform->EnableInputThrottle(true);

  ComPtr<IMFAttributes> attributes = media_transform->GetAttributes();
  if (!attributes) {
    // Decoder Transform setup failed
    return scoped_ptr<MediaTransform>().Pass();
  }

  UINT32 is_d3d_aware_attribute = false;
  HRESULT hr = attributes->GetUINT32(MF_SA_D3D_AWARE, &is_d3d_aware_attribute);
  if (SUCCEEDED(hr) && is_d3d_aware_attribute) {
    // Ignore the return value, an error is expected when running in Session 0.
    hr = media_transform->SendMessage(MFT_MESSAGE_SET_D3D_MANAGER,
                                      ULONG_PTR(device_manager));
    if (FAILED(hr)) {
      SB_LOG(WARNING) << "Unable to set device manager for d3d aware decoder, "
                         "disabling DXVA.";
      hr = attributes->SetUINT32(CODECAPI_AVDecVideoAcceleration_H264, FALSE);
      if (FAILED(hr)) {
        SB_LOG(WARNING) << "Unable to disable DXVA.";
        return scoped_ptr<MediaTransform>().Pass();
      }
    } else {
      hr = attributes->SetUINT32(CODECAPI_AVDecVideoAcceleration_H264, TRUE);
      if (FAILED(hr)) {
        SB_LOG(INFO) << "Unable to enable DXVA for video decoder.";
      }
    }
  } else {
    SB_LOG(WARNING) << "Video decoder is not D3D aware, decoding may be slow.";
  }

  // Tell the decoder to allocate resources for the maximum resolution in
  // order to minimize glitching on resolution changes.
  if (FAILED(attributes->SetUINT32(MF_MT_DECODER_USE_MAX_RESOLUTION, 1))) {
    return scoped_ptr<MediaTransform>().Pass();
  }

  ComPtr<IMFMediaType> input_type;
  if (FAILED(MFCreateMediaType(&input_type)) || !input_type) {
    return scoped_ptr<MediaTransform>().Pass();
  }
  CheckResult(input_type->SetGUID(MF_MT_MAJOR_TYPE, MFMediaType_Video));
  CheckResult(input_type->SetGUID(MF_MT_SUBTYPE, input_guid));
  CheckResult(input_type->SetUINT32(MF_MT_INTERLACE_MODE,
                                    MFVideoInterlace_Progressive));
  if (input_guid == MFVideoFormat_VP90) {
    // Set the expected video resolution. Setting the proper resolution can
    // mitigate a format change, but the decoder will adjust to the real
    // resolution regardless.
    CheckResult(MFSetAttributeSize(input_type.Get(), MF_MT_FRAME_SIZE,
                                   kMaxDecodeTargetWidth,
                                   kMaxDecodeTargetHeight));
  }
  media_transform->SetInputType(input_type);

  media_transform->SetOutputTypeBySubType(output_guid);

  return media_transform.Pass();
}

class VideoFrameImpl : public VideoFrame {
 public:
  VideoFrameImpl(SbTime timestamp, std::function<void(VideoFrame*)> release_cb)
      : VideoFrame(timestamp), release_cb_(release_cb) {
    SB_DCHECK(release_cb_);
  }
  ~VideoFrameImpl() { release_cb_(this); }

 private:
  std::function<void(VideoFrame*)> release_cb_;
};

}  // namespace

VideoDecoder::VideoDecoder(
    SbMediaVideoCodec video_codec,
    SbPlayerOutputMode output_mode,
    SbDecodeTargetGraphicsContextProvider* graphics_context_provider,
    SbDrmSystem drm_system,
    bool is_hdr_supported)
    : video_codec_(video_codec),
      graphics_context_provider_(graphics_context_provider),
      drm_system_(drm_system),
      is_hdr_supported_(is_hdr_supported) {
  SB_DCHECK(output_mode == kSbPlayerOutputModeDecodeToTexture);

  HardwareDecoderContext hardware_context = GetDirectXForHardwareDecoding();
  d3d_device_ = hardware_context.dx_device_out;
  device_manager_ = hardware_context.dxgi_device_manager_out;
  HRESULT hr = d3d_device_.As(&video_device_);
  if (FAILED(hr)) {
    return;
  }

  ComPtr<ID3D11DeviceContext> d3d_context;
  d3d_device_->GetImmediateContext(d3d_context.GetAddressOf());
  d3d_context.As(&video_context_);
}

VideoDecoder::~VideoDecoder() {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  Reset();
  ShutdownCodec();
}

// static
bool VideoDecoder::IsHardwareVp9DecoderSupported(bool is_hdr_required) {
  static bool s_first_time_update = true;
  static bool s_is_vp9_supported = false;
  static bool s_is_hdr_supported = false;

  const UINT D3D11_VIDEO_DECODER_CAPS_UNSUPPORTED = 0x10;

  if (s_first_time_update) {
    ComPtr<ID3D11Device> d3d11_device;
    HRESULT hr = D3D11CreateDevice(
        nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, nullptr, 0,
        D3D11_SDK_VERSION, d3d11_device.GetAddressOf(), nullptr, nullptr);
    if (FAILED(hr)) {
      return false;
    }
    ComPtr<ID3D11VideoDevice1> video_device;
    if (FAILED(d3d11_device.As(&video_device))) {
      return false;
    }
    const DXGI_RATIONAL kFps = {30, 1};  // 30 fps = 30/1
    const UINT kBitrate = 0;
    UINT caps_profile_0 = 0;
    if (SUCCEEDED(video_device->GetVideoDecoderCaps(&DXVA_ModeVP9_VLD_Profile0,
                                                    3840, 2160, &kFps, kBitrate,
                                                    NULL, &caps_profile_0))) {
      s_is_vp9_supported =
          caps_profile_0 != D3D11_VIDEO_DECODER_CAPS_UNSUPPORTED;
    }

    UINT caps_profile_2 = 0;
    if (SUCCEEDED(video_device->GetVideoDecoderCaps(
            &DXVA_ModeVP9_VLD_10bit_Profile2, 3840, 2160, &kFps, kBitrate, NULL,
            &caps_profile_2))) {
      s_is_hdr_supported =
          caps_profile_2 != D3D11_VIDEO_DECODER_CAPS_UNSUPPORTED;
    }
    s_first_time_update = false;
  }
  return is_hdr_required ? s_is_vp9_supported && s_is_hdr_supported
                         : s_is_vp9_supported;
}

size_t VideoDecoder::GetPrerollFrameCount() const {
  return kMaxOutputSamples;
}

size_t VideoDecoder::GetMaxNumberOfCachedFrames() const {
  return kMaxOutputSamples;
}

void VideoDecoder::Initialize(const DecoderStatusCB& decoder_status_cb,
                              const ErrorCB& error_cb) {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  SB_DCHECK(!decoder_status_cb_);
  SB_DCHECK(decoder_status_cb);
  SB_DCHECK(!error_cb_);
  SB_DCHECK(error_cb);
  decoder_status_cb_ = decoder_status_cb;
  error_cb_ = error_cb;
  if (video_device_) {
    InitializeCodec();
  }
  if (!decoder_) {
    error_cb_(kSbPlayerErrorDecode, "Cannot initialize codec.");
  }
}

void VideoDecoder::WriteInputBuffer(
    const scoped_refptr<InputBuffer>& input_buffer) {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  SB_DCHECK(input_buffer);
  SB_DCHECK(decoder_status_cb_);
  EnsureDecoderThreadRunning();

  if (TryUpdateOutputForHdrVideo(input_buffer->video_sample_info())) {
    ScopedLock lock(thread_lock_);
    thread_events_.emplace_back(
        new Event{Event::kWriteInputBuffer, input_buffer});
  } else {
    error_cb_(kSbPlayerErrorCapabilityChanged,
              "HDR sink lost while HDR video playing.");
  }
}

void VideoDecoder::WriteEndOfStream() {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  SB_DCHECK(decoder_status_cb_);
  EnsureDecoderThreadRunning();

  ScopedLock lock(thread_lock_);
  thread_events_.emplace_back(new Event{Event::kWriteEndOfStream});
}

void VideoDecoder::Reset() {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  StopDecoderThread();

  // Make sure all output samples have been released before flushing the
  // decoder. Be sure to Acquire the mutexes in the same order as
  // CreateDecodeTarget to avoid possible deadlock.
  outputs_reset_lock_.Acquire();
  thread_lock_.Acquire();
  thread_outputs_.clear();
  thread_lock_.Release();
  outputs_reset_lock_.Release();

  // If the previous priming hasn't finished, restart it.  This happens rarely
  // as it is only triggered when a seek is requested immediately after video is
  // started.
  if (priming_output_count_ > 0) {
    priming_output_count_ = kVp9PrimingFrameCount;
  }

  decoder_status_cb_(kReleaseAllFrames, nullptr);
  if (decoder_) {
    decoder_->Reset();
  }
}

SbDecodeTarget VideoDecoder::GetCurrentDecodeTarget() {
  auto decode_target = CreateDecodeTarget();

  if (SbDecodeTargetIsValid(decode_target)) {
    if (SbDecodeTargetIsValid(current_decode_target_)) {
      prev_decode_targets_.emplace_back(current_decode_target_);
    }
    current_decode_target_ = decode_target;
  }
  if (SbDecodeTargetIsValid(current_decode_target_)) {
    // Add a reference for the caller.
    current_decode_target_->AddRef();
  }
  return current_decode_target_;
}

SbDecodeTarget VideoDecoder::CreateDecodeTarget() {
  RECT video_area;
  ComPtr<IMFSample> video_sample;

  // Don't allow a decoder reset (flush) while an IMFSample is
  // alive. However, the decoder thread should be allowed to continue
  // while the SbDecodeTarget is being created.
  ScopedLock reset_lock(outputs_reset_lock_);

  // Use the oldest output.
  thread_lock_.Acquire();
  if (!thread_outputs_.empty()) {
    // This function should not remove output frames. However, it's possible
    // for the same frame to be requested multiple times. To avoid re-creating
    // SbDecodeTargets, release the video_sample once it is used to create
    // an output frame. The next call to CreateDecodeTarget for the same frame
    // will return kSbDecodeTargetInvalid, and |current_decode_target_| will
    // be reused.
    Output& output = thread_outputs_.front();
    video_area = output.video_area;
    video_sample.Swap(output.video_sample);
  }
  thread_lock_.Release();

  SbDecodeTarget decode_target = kSbDecodeTargetInvalid;
  if (video_sample != nullptr) {
    // Try reusing the previous decode target to avoid the performance hit of
    // creating a new texture.
    SB_DCHECK(prev_decode_targets_.size() <= kDecodeTargetCacheSize + 1);
    if (prev_decode_targets_.size() >= kDecodeTargetCacheSize) {
      decode_target = prev_decode_targets_.front();
      prev_decode_targets_.pop_front();
      auto hardware_decode_target =
          reinterpret_cast<HardwareDecodeTargetPrivate*>(decode_target);
      if (!hardware_decode_target->Update(
              d3d_device_, video_device_, video_context_, video_enumerator_,
              video_processor_, video_sample, video_area, is_hdr_supported_)) {
        // The cached decode target was not compatible; just release it.
        SbDecodeTargetRelease(decode_target);
        decode_target = kSbDecodeTargetInvalid;
      }
    }

    if (!SbDecodeTargetIsValid(decode_target)) {
      decode_target = new HardwareDecodeTargetPrivate(
          d3d_device_, video_device_, video_context_, video_enumerator_,
          video_processor_, video_sample, video_area, is_hdr_supported_);
    }

    // Release the video_sample before releasing the reset lock.
    video_sample.Reset();
  }
  return decode_target;
}

void VideoDecoder::InitializeCodec() {
  scoped_ptr<MediaTransform> media_transform;

  // If this is updated then media_is_video_supported.cc also needs to be
  // updated.
  switch (video_codec_) {
    case kSbMediaVideoCodecH264: {
      media_transform =
          CreateVideoTransform(CLSID_MSH264DecoderMFT, MFVideoFormat_H264,
                               MFVideoFormat_NV12, device_manager_.Get());
      priming_output_count_ = 0;
      if (!media_transform) {
        SB_LOG(WARNING) << "H264 hardware decoder creation failed.";
        return;
      }
      break;
    }
    case kSbMediaVideoCodecVp9: {
      if (IsHardwareVp9DecoderSupported()) {
        media_transform =
            CreateVideoTransform(CLSID_MSVPxDecoder, MFVideoFormat_VP90,
                                 MFVideoFormat_NV12, device_manager_.Get());
        priming_output_count_ = kVp9PrimingFrameCount;
      }
      if (!media_transform) {
        SB_LOG(WARNING) << "VP9 hardware decoder creation failed.";
        return;
      }
      break;
    }
    default: { SB_NOTREACHED(); }
  }

  decoder_.reset(
      new DecryptingDecoder("video", media_transform.Pass(), drm_system_));
  MediaTransform* transform = decoder_->GetDecoder();

  DWORD input_stream_count = 0;
  DWORD output_stream_count = 0;
  SB_DCHECK(transform);
  transform->GetStreamCount(&input_stream_count, &output_stream_count);
  SB_DCHECK(1 == input_stream_count);
  SB_DCHECK(1 == output_stream_count);

  ComPtr<IMFAttributes> attributes = transform->GetAttributes();
  SB_DCHECK(attributes);
  CheckResult(attributes->SetUINT32(MF_SA_MINIMUM_OUTPUT_SAMPLE_COUNT,
                                    kMaxOutputSamples));

  UpdateVideoArea(transform->GetCurrentOutputType());

  // The transform must output textures that are bound to shader resources,
  // or we can't draw them later via ANGLE.
  ComPtr<IMFAttributes> output_attributes =
      transform->GetOutputStreamAttributes();
  SB_DCHECK(output_attributes);
  CheckResult(output_attributes->SetUINT32(
      MF_SA_D3D11_BINDFLAGS, D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_DECODER));

  // The resolution and framerate will adjust to the actual content data.
  D3D11_VIDEO_PROCESSOR_CONTENT_DESC content_desc = {};
  content_desc.InputFrameFormat = D3D11_VIDEO_FRAME_FORMAT_PROGRESSIVE;
  content_desc.InputFrameRate.Numerator = 60;
  content_desc.InputFrameRate.Denominator = 1;
  content_desc.InputWidth = kMaxDecodeTargetWidth;
  content_desc.InputHeight = kMaxDecodeTargetHeight;
  content_desc.OutputFrameRate.Numerator = 60;
  content_desc.OutputFrameRate.Denominator = 1;
  content_desc.OutputWidth = kMaxDecodeTargetWidth;
  content_desc.OutputHeight = kMaxDecodeTargetHeight;
  content_desc.Usage = D3D11_VIDEO_USAGE_PLAYBACK_NORMAL;
  CheckResult(video_device_->CreateVideoProcessorEnumerator(
      &content_desc, video_enumerator_.GetAddressOf()));
  CheckResult(video_device_->CreateVideoProcessor(
      video_enumerator_.Get(), 0, video_processor_.GetAddressOf()));
  SB_DCHECK(video_context_);
  video_context_->VideoProcessorSetStreamFrameFormat(
      video_processor_.Get(), MediaTransform::kStreamId,
      D3D11_VIDEO_FRAME_FORMAT_PROGRESSIVE);
  video_context_->VideoProcessorSetStreamAutoProcessingMode(
      video_processor_.Get(), 0, false);
}

void VideoDecoder::ShutdownCodec() {
  SB_DCHECK(!SbThreadIsValid(decoder_thread_));
  SB_DCHECK(thread_outputs_.empty());
  if (!decoder_) {
    return;
  }

  // Work around a VP9 decoder crash. All IMFSamples and anything that may
  // reference them indirectly (the d3d texture in SbDecodeTarget) must be
  // released before releasing the IMFTransform. Do this on the render thread
  // since graphics resources are being released.
  graphics_context_provider_->gles_context_runner(
      graphics_context_provider_, &VideoDecoder::ReleaseDecodeTargets, this);

  // Microsoft recommends stalling to let other systems release their
  // references to the IMFSamples.
  if (video_codec_ == kSbMediaVideoCodecVp9) {
    SbThreadSleep(150 * kSbTimeMillisecond);
  }
  decoder_.reset();
  video_processor_.Reset();
  video_enumerator_.Reset();
}

// static
void VideoDecoder::ReleaseDecodeTargets(void* context) {
  VideoDecoder* this_ptr = static_cast<VideoDecoder*>(context);
  while (!this_ptr->prev_decode_targets_.empty()) {
    SbDecodeTargetRelease(this_ptr->prev_decode_targets_.front());
    this_ptr->prev_decode_targets_.pop_front();
  }
  if (SbDecodeTargetIsValid(this_ptr->current_decode_target_)) {
    SbDecodeTargetRelease(this_ptr->current_decode_target_);
    this_ptr->current_decode_target_ = kSbDecodeTargetInvalid;
  }
}

void VideoDecoder::EnsureDecoderThreadRunning() {
  SB_DCHECK(thread_checker_.CalledOnValidThread());

  // NOTE: The video decoder thread will exit after processing the
  // kWriteEndOfStream event. In this case, Reset must be called (which will
  // then StopDecoderThread) before WriteInputBuffer or WriteEndOfStream again.
  SB_DCHECK(!decoder_thread_stopped_);

  if (!SbThreadIsValid(decoder_thread_)) {
    if (!decoder_) {
      error_cb_(kSbPlayerErrorDecode, "Decoder is not valid.");
      return;
    }
    SB_DCHECK(decoder_ != nullptr);
    SB_DCHECK(thread_events_.empty());
    decoder_thread_stop_requested_ = false;
    decoder_thread_ =
        SbThreadCreate(0, kSbThreadPriorityHigh, kSbThreadNoAffinity, true,
                       "VideoDecoder", &VideoDecoder::DecoderThreadEntry, this);
    SB_DCHECK(SbThreadIsValid(decoder_thread_));
  }
}

void VideoDecoder::StopDecoderThread() {
  SB_DCHECK(thread_checker_.CalledOnValidThread());
  if (SbThreadIsValid(decoder_thread_)) {
    decoder_thread_stop_requested_ = true;
    SbThreadJoin(decoder_thread_, nullptr);
    SB_DCHECK(decoder_thread_stopped_);
    decoder_thread_stopped_ = false;
    decoder_thread_ = kSbThreadInvalid;
  }
  thread_events_.clear();
}

void VideoDecoder::UpdateVideoArea(const ComPtr<IMFMediaType>& media) {
  MFVideoArea video_area;
  HRESULT hr = media->GetBlob(MF_MT_MINIMUM_DISPLAY_APERTURE,
                              reinterpret_cast<UINT8*>(&video_area),
                              sizeof(video_area), nullptr);
  if (SUCCEEDED(hr)) {
    video_area_.left = video_area.OffsetX.value;
    video_area_.top = video_area.OffsetY.value;
    video_area_.right = video_area_.left + video_area.Area.cx;
    video_area_.bottom = video_area_.top + video_area.Area.cy;
    return;
  }

  UINT32 width;
  UINT32 height;
  hr = MFGetAttributeSize(media.Get(), MF_MT_FRAME_SIZE, &width, &height);
  if (SUCCEEDED(hr)) {
    video_area_.left = 0;
    video_area_.top = 0;
    video_area_.right = width;
    video_area_.bottom = height;
    return;
  }

  SB_NOTREACHED() << "Could not determine new video output resolution";
}

scoped_refptr<VideoFrame> VideoDecoder::CreateVideoFrame(
    const ComPtr<IMFSample>& sample) {
  // NOTE: All samples must be released before flushing the decoder. Since
  // the host may hang onto VideoFrames that are created here, make them
  // weak references to the actual sample.
  LONGLONG win32_sample_time = 0;
  CheckResult(sample->GetSampleTime(&win32_sample_time));
  SbTime sample_time = ConvertToSbTime(win32_sample_time);

  thread_lock_.Acquire();
  thread_outputs_.emplace_back(sample_time, video_area_, sample);
  thread_lock_.Release();

  // The "native texture" for the VideoFrame is actually just the timestamp
  // for the output sample.
  return new VideoFrameImpl(
      sample_time, std::bind(&VideoDecoder::DeleteVideoFrame, this, _1));
}

void VideoDecoder::DeleteVideoFrame(VideoFrame* video_frame) {
  ScopedLock lock(thread_lock_);
  for (auto iter = thread_outputs_.begin(); iter != thread_outputs_.end();
       ++iter) {
    if (iter->time == video_frame->timestamp()) {
      thread_outputs_.erase(iter);
      break;
    }
  }
}

void VideoDecoder::DecoderThreadRun() {
  std::list<std::unique_ptr<Event> > priming_events;
  std::unique_ptr<Event> event;
  bool is_end_of_stream = false;

  while (!decoder_thread_stop_requested_) {
    int outputs_to_process = 1;
    bool wrote_input = false;
    bool read_output = false;

    // Process a new event or re-try the previous event.
    if (event == nullptr) {
      ScopedLock lock(thread_lock_);
      if (!thread_events_.empty()) {
        event.swap(thread_events_.front());
        thread_events_.pop_front();
      }
    }

    if (event == nullptr) {
      SbThreadSleep(kSbTimeMillisecond);
    } else {
      switch (event->type) {
        case Event::kWriteInputBuffer:
          SB_DCHECK(event->input_buffer != nullptr);
          if (decoder_->TryWriteInputBuffer(event->input_buffer, 0)) {
            if (priming_output_count_ > 0) {
              // Save this event for the actual playback.
              priming_events.emplace_back(event.release());
            }
            // The event was successfully processed. Discard it.
            event.reset();
            wrote_input = true;
          } else {
            // The decoder must be full. Re-try the event on the next
            // iteration. Additionally, try reading an extra output frame to
            // start draining the decoder.
            ++outputs_to_process;
          }
          break;
        case Event::kWriteEndOfStream:
          if (priming_output_count_ > 0) {
            // Finish priming when eos is encountered.
            priming_output_count_ = 0;
            thread_lock_.Acquire();
            while (!priming_events.empty()) {
              thread_events_.emplace_front(priming_events.back().release());
              priming_events.pop_back();
            }
            // Also append the eos event.
            thread_events_.emplace_back(event.release());
            thread_lock_.Release();
            decoder_->Reset();
            break;
          }
          event.reset();
          decoder_->Drain();
          is_end_of_stream = true;
          wrote_input = true;
          break;
      }
    }

    // Process output frame(s).
    for (int outputs = 0; outputs < outputs_to_process; ++outputs) {
      // NOTE: IMFTransform::ProcessOutput (called by decoder_->ProcessAndRead)
      // may stall if the number of active IMFSamples would exceed the value of
      // MF_SA_MINIMUM_OUTPUT_SAMPLE_COUNT.
      thread_lock_.Acquire();
      bool input_full = thread_events_.size() >= kMaxInputSamples;
      bool output_full = thread_outputs_.size() >= kMaxOutputSamples;
      thread_lock_.Release();

      Status status = input_full ? kBufferFull : kNeedMoreInput;
      decoder_status_cb_(status, nullptr);

      if (output_full) {
        // Wait for the active samples to be consumed before polling for more.
        break;
      }

      ComPtr<IMFSample> sample;
      ComPtr<IMFMediaType> media_type;
      decoder_->ProcessAndRead(&sample, &media_type);
      if (media_type) {
        UpdateVideoArea(media_type);
      }
      if (sample) {
        if (priming_output_count_ > 0) {
          // Ignore the output samples while priming the decoder.
          if (--priming_output_count_ == 0) {
            // Replay all the priming events once priming is finished.
            if (event != nullptr) {
              priming_events.emplace_back(event.release());
            }
            thread_lock_.Acquire();
            while (!priming_events.empty()) {
              thread_events_.emplace_front(priming_events.back().release());
              priming_events.pop_back();
            }
            thread_lock_.Release();
            decoder_->Reset();
          }
        } else {
          decoder_status_cb_(status, CreateVideoFrame(sample));
        }
        read_output = true;
      } else if (is_end_of_stream) {
        decoder_status_cb_(kBufferFull, VideoFrame::CreateEOSFrame());
        return;
      }
    }

    if (!wrote_input && !read_output) {
      // Throttle decode loop since no I/O was possible.
      SbThreadSleep(kSbTimeMillisecond);
    }
  }
}

// static
void* VideoDecoder::DecoderThreadEntry(void* context) {
  SB_DCHECK(context);
  VideoDecoder* decoder = static_cast<VideoDecoder*>(context);
  decoder->DecoderThreadRun();
  decoder->decoder_thread_stopped_ = true;
  return nullptr;
}

}  // namespace win32
}  // namespace shared
}  // namespace starboard